Dual-modal imaging techniques have gained intense attention for their potential role in the dawning era of tumor early accurate diagnosis. Chelate-free robust dual-modal imaging nanoprobes with high efficiency and low toxicity are of essential importance for tumor targeted dual-modal in vivo imaging. It is still a crucial issue to endow Cd-free dual-modal nanoprobes with bright fluorescence as well as high relaxivity. Herein, a facile synthetic strategy was developed to prepare Gd-doped CuInS/ZnS bimodal quantum dots (GCIS/ZnS, BQDs) with optimized properties. The fluorescent properties of the GCIS/ZnS BQDs can be thoroughly optimized by varying reaction temperature, aging time, and ZnS coating. The amount of Gd precursor can be well-controlled to realize the optimized balance between the MR relaxivity and optical properties. The obtained hydrophobic GCIS/ZnS BQDs were surface engineered into aqueous phase with PEGylated dextran-stearyl acid polymeric lipid vesicles (PEG-DS PLVs). Upon the phase transfer, the hydrophilic GCIS/ZnS@PLVs exhibited pronounced near-infrared fluorescence as well as high longitudinal relaxivity (r1 = 9.45 mM(-1) S(-1)) in water with good colloidal stability. In vivo tumor-bearing animal experiments further verified GCIS/ZnS@PLVs could achieve tumor-targeted MR/fluorescence dual-modal imaging. No toxicity was observed in the in vivo and ex vivo experiments. The GCIS/ZnS@PLVs present great potential as bimodal imaging contrast agents for tumor diagnosis.
Keywords: MRI; dual-modal imaging; fluorescence imaging; quantum dots; targeted imaging.